1. Field of the Invention
The present invention relates to an electrotherapy unit. In particular, the present invention relates to a full-range electrotherapy unit with a digital force modutator.
2. Description of the Related Art
Electrotherapy units comprise low frequency (lower than 1 kHz) types, medium frequency (1 kHz–5 kHz) types, and high frequency (above 5 kHz) types. The electrotherapy units include conductive pads to be in contact with the skin of a person receiving electric therapy by means of outputting low-frequency, medium-frequency, or high-frequency voltage to provide the human body with an electric stimulating effect.
FIG. 8 of the drawings illustrates a conventional electrotherapy unit comprising an analog power supply 10′, an AM signal generator 20′, an FM signal generator 30′, an analog signal mixer 40′, an analog power amplifier 50′, a voltage-increasing transformer 60′, and two conductive pads 70′. The analog power supply 10′ supplies power to the analog power amplifier 50′. Input signals from the AM signal generator 20′ or the FM signal generator 30′ are inputted to the analog signal mixer 40′ to create a medium-frequency vibrating voltage which is amplified by the analog power amplifier 50′ and then increased by the voltage-increasing transformer 60′. An amplified AM or FM medium-frequency voltage is generated and outputted through the conductive pads 70′ to provide the human body with an electric stimulating effect.
The analog power amplifier 50′ is substantially an amplifying circuit consisting of an operational amplifier and two power transistors for amplifying the inputted voltage. The collector of each power transistor is connected to a primary coil of the voltage-increasing transformer 60′. However, the rectilinear analog power amplifier 50′ has a relatively large power loss due to the temperature of the transistors, setting of the transistors, VCE voltage, current leakage, etc. Further, the electric circuit is apt to consume larger power and fails to provide a stable frequency under high frequency, as high-frequency parasitical oscillation is apt to be generated by a parasitical capacitor in the transistor. As a result, the electrotherapy unit could not be used in high frequency.
Further, since the collector of each transistor is connected to the primary coil of the voltage-increasing transformer that has an inductance, the reverse electromotive generated by the primary coil during reversion of the voltage would directly flow into the transistor, resulting in damage to the transistors.